Lubricant oil composition

ABSTRACT

Provided is a lubricating oil composition, which is used in an internal combustion engine employing a fuel containing at least one kind selected from a hydrogenated product of natural fats and oils, a transesterification product of natural fats and oils, and a hydrogenated product of a transesterification product of natural fats and oils, which includes an alkali metal borate or a hydrate thereof in an alkali metal-corresponding amount of 10 to 1,000 ppm by mass in terms of total amount of the lubricating oil composition, and which can satisfactorily exhibit cleanness even in the case where the above-mentioned fuel is mixed therein or the case where ash content thereof is low.

REFERENCE TO PRIOR APPLICATIONS

This application is a Division of U.S. application Ser. No. 12/681,864, filed Apr. 6, 2010; which is a 371 of PCT/JP2008/067099, filed Sep. 22, 2008. Priority to Japanese patent application 2007-269380, filed Oct. 16, 2007, is claimed.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for an internal combustion engine employing a so-called biofuel containing a transesterification reaction product of natural fats and oils, or the like.

BACKGROUND ART

In recent years, it has been an important issue, regarding the pollution caused by automobile exhaust gas, to take a countermeasure for reducing environmental pollution caused by exhaust gas components such as particulate matters (PM: fine particles) and NO_(x) which are exhausted from an internal combustion engine, and in particular, from a diesel engine.

As a countermeasure therefor, installation of an exhaust gas purification device such as a diesel particulate filter (DPF) or an exhaust gas purification catalyst (oxidation or reduction catalyst) to an automobile has thus been a promising solution.

However, in the case where a conventional lubricating oil composition for an internal combustion engine is used in an automobile mounted with the exhaust gas purification device, the following problems need to be solved. First, soot adheres to the particulate filter. The adhered soot is removed by oxidation and combustion, but in general, a post injection of the fuel is performed in order to burn the soot. Accordingly, fuel dilution to an engine oil is increased, whereby a performance of the engine oil is lowered.

Further, metal oxides, sulfates, carboxylates, and the like, which are generated by combustion, cause clogging of the filter. Therefore, it is preferred that a metal content in the lubricating oil be as small as possible, but it is difficult to decrease an amount of the metal while maintaining detergency and oxidation stability, because the metal content is derived mainly from a metal-based detergent and an antioxidant.

In view of solving the above-mentioned problems, many proposals have been made. For example, there is disclosed a lubricating oil composition for a diesel engine equipped with DPF, which is capable of decreasing ash clogging in DPF, improving combustibility of PM collected by DPF to thereby increase removal efficiency of PM, and lengthening lifetime of DPF, that is, a lubricating oil composition for a diesel engine equipped with a diesel fine-particle-removing device having a feature of containing a sulfated ash content of 1.0 wt % or less, a sulfur content of 0.3 wt % or less, and a molybdenum content of 100 ppm or more (for example, refer to Patent Document 1).

On the other hand, as for the fuel used in automobiles, a so-called biofuel has been drawing attention from the viewpoint of decreasing carbon dioxide which is a main cause for global warming.

The biofuel is a fuel containing compounds derived from natural fats and oils such as a transesterification reaction product of natural fats and oils, and also, there is a provision that carbon dioxide generated from the biofuel is carbon neutral, which is not counted as an increase in greenhouse gas, because plants to be a source of natural fats and oils grow through photosynthesis by absorbing carbon dioxide in the atmosphere. Therefore, it is presumed that utilization of the biofuel will further increase.

When such a biofuel is used in an automobile mounted with the particulate filter, in addition to performance deterioration of engine oil due to increase in fuel dilution to the engine oil, decrease in oxidation stability of the engine oil occurs and influence to detergency of engine parts becomes large, because polar compounds and the like are generated from degradation and decomposition of the biofuel. The fact becomes a problem which is further difficult to solve in the case where the metal content in the lubricating oil is decreased in order to avoid clogging of the filter.

-   Patent Document 1: JP 2002-60776 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention provides a lubricating oil composition used in an internal combustion engine employing a biofuel, and an object of the present invention is to provide a lubricating oil composition which can satisfactorily exhibit detergency even in the case where the biofuel is mixed therein or the case where ash content thereof is low.

Means for Solving the Problems

The inventors of the present invention have found that a lubricating oil composition mixed with a specific compound has an effect of suppressing deterioration of performances such as detergency of the lubricating oil even in the case where the biofuel is mixed therein, and thus, the object of the present invention can be achieved. The present invention has been accomplished in view of the above finding.

That is, the present invention provides:

[1] a lubricating oil composition, which is used in an internal combustion engine employing a fuel containing at least one kind selected from a hydrogenated product of natural fats and oils, a transesterification product of natural fats and oils, and a hydrogenated product of a transesterification product of natural fats and oils, the lubricating oil composition including an alkali metal borate or a hydrate thereof in an amount of 10 to 1,000 ppm by mass in terms of an alkali metal, based on a total amount of the lubricating oil composition;

[2] a lubricating oil composition according to the item [1], further including, in addition to (A) the alkali metal borate or the hydrate thereof, at least one kind selected from the following (B) to (E):

(B) at least one kind of compound selected from:

-   -   a substituted hydroxyaromatic carboxylate derivative represented         by the following general formula (I):

-   -   where: R¹ and R², which may be identical to or different from         each other, each represent an organic group having 6 or more         carbon atoms; a, b, c, d, and e each represent an integer         satisfying relations of 1≦a≦3, 1≦b≦3, 0≦c≦3, 1≦d≦3, 1≦e≦3,         3≦(a+b+e)≦6, and 1≦(c+d)≦5; and when a plurality of R¹'s and a         plurality of R²'s are present, each of the plurality of R¹'s and         the plurality of R²'s may be identical to or different from one         another within the respective groups; and

a substituted hydroxyaromatic carboxylate derivative represented by the following general formula (II):

-   -   where: R³, R⁴, and R⁵, which may be identical to or different         from one another, each represent an organic group having 6 or         more carbon atoms; f, g, h, i, j, k, and m each represent an         integer satisfying relations of 0≦f≦3, 0≦g≦3, 1≦(f+g)≦3, 0≦h≦4,         0≦i≦3, 1≦(h+i)≦6, 0≦j≦3, 1≦k≦3, 1≦m≦3, 0≦(f+h)≦4, 1≦(g+i+m)≦4,         and 1≦(j+k)≦5; and when a plurality of R³'s, a plurality of         R⁴'s, and a plurality of R⁵'s are present, each of the plurality         of R³'s, the plurality of R⁴'s, and the plurality of R⁵'s may be         identical to or different from one another within the respective         groups;

(C) a phenol-based antioxidant;

(D) an amine-based antioxidant; and

(E) a molybdenum-based antioxidant; and

[3] a lubricating oil composition according to the item [1] or [2], including a sulfated ash content of 1.2 mass % or less.

Effects of the Invention

The lubricating oil composition of the present invention is used for the internal combustion engine employing a biofuel, and the present invention can provide the lubricating oil composition which can satisfactorily exhibit detergency even in the case where the biofuel is mixed therein or the case where ash content thereof is low.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention provides a lubricating oil composition, which is used in an internal combustion engine employing a fuel containing at least one kind selected from natural fats and oils, a hydrogenated product of natural fats and oils, a transesterification product of natural fats and oils, and a hydrogenated product of a transesterification product of natural fats and oils.

Here, examples of the natural fats and oils which may be used include various kinds of flora and fauna fats and oils existing in the natural environment. However, vegetable oils having, as main components, esters derived from aliphatic acid and glycerine such as a safflower oil, soybean oil, rapeseed oil, palm oil, palm kernel oil, cotton oil, coconut oil, rice bran oil, sesame oil, castor oil, linseed oil, olive oil, tung oil, camellia oil, peanut oil, kapok oil, cacao oil, sumac wax, sunflower oil, and corn oil are preferably used.

The hydrogenated product of natural fats and oils is a product in which the above-mentioned fats and oils are subjected to so-called hydrogenation under the presence of an appropriate hydrogenation catalyst.

Here, examples of the hydrogenation catalyst include a nickel-based catalyst, a platinum group (Pt, Pd, Rh, and Ru)-based catalyst, a cobalt-based catalyst, a chrome oxide-based catalyst, a copper-based catalyst, an osmium-based catalyst, an iridium-based catalyst, and a molybdenum-based catalyst. Further, it is also preferred that those catalysts be used in combination of two or more as the hydrogenation catalyst.

The transesterification product of natural fats and oils is an ester obtained by transesterification with triglyceride which forms natural fats and oils under the presence of an appropriate ester synthesis catalyst. For example, lower alcohol and natural fats and oils are subjected to transesterification under the presence of the ester synthesis catalyst, whereby aliphatic acid ester to be a biofuel is produced. The lower alcohol is used as an esterifying agent, and examples thereof include methanol, ethanol, propanol, butanol, and pentanol, those of which are alcohols each having 5 or less carbon atoms. However, from the viewpoints of reactivity and cost, methanol is preferred. Those lower alcohols are generally used in an equivalent amount or an amount more than the equivalent amount with respect to the fats and oils.

Further, the hydrogenated product of a transesterification product of natural fats and oils is a product in which the above-mentioned transesterification product of natural fats and oils are subjected to hydrogenation under the presence of an appropriate hydrogenation catalyst.

The natural fats and oils, the hydrogenated product of natural fats and oils, the transesterification product of natural fats and oils, and the hydrogenated product of a transesterification product of natural fats and oils can each be added to a fuel formed of hydrocarbon such as light oil to thereby be favorably used as a composite fuel.

A base oil according to the lubricating oil composition of the present invention is not particularly limited, and any appropriate mineral oil and synthetic oil, which are conventionally used as a base oil of the lubricating oil composition for the internal combustion engine, can be appropriately selected and used.

Examples of the mineral oil include: a mineral oil purified by subjecting lubricating oil fraction, which is obtained by vacuum distillating the residual oil at normal pressure given by the atmospheric distillation of crude oil, to one or more treatments selected from solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydrorefining, and the like; and a mineral oil produced by isomerization of wax or GTL WAX.

Further, examples of the synthetic oil include polybutene, polyolefin [α-olefinhomopolymers and copolymers (such as ethylene-α-olefin copolymers), and the like], various kinds of esters (such as polyol ester, dibasic acid esters, and phosphate esters), various kinds of ethers (such as polyphenyl ether and the like), polyglycol, alkylbenzene, and alkylnaphthalene. Of those synthetic oils, polyolefins and polyol esters are particularly preferable.

In the present invention, the above mineral oils may be used alone or in combination of two or more kinds as the base oil. Further, the above synthetic oils may be used alone or in combination of two or more kinds as the base oil. Still further, one or more kinds of the mineral oils and one or more kinds of the synthetic oils may be used in combination as the base oil.

A viscosity of the base oil is not particularly limited and differs depending on intended use of the lubricating oil composition, but in general, a kinematic viscosity of the base oil at 100° C. is 2 to 30 mm²/s, preferably 3 to 15 mm²/s, and more preferably 4 to 10 mm²/s. When the kinematic viscosity of the base oil at 100° C. is 2 mm²/s or more, evaporation loss thereof is small, and on the other hand, when the kinematic viscosity is 30 mm²/s or less, dynamic loss thereof due to viscosity resistance does not become too large, whereby improvement effect in fuel consumption can be obtained.

Further, as the base oil, a base oil in which % C_(A) measured through ring analysis is 3.0 or less and sulfur content is 50 ppm by mass or less is preferably used. Here, the % C_(A) measured through ring analysis refers to a ratio (percentage) of an aromatic component content calculated in accordance with ring analysis n-d-M method. Further, the sulfur content is a value measured in accordance with JIS K 2541.

The base oil in which the % C_(A) is 3.0 or less and the sulfur content is 50 ppm by mass or less has satisfactory oxidation stability. Thus, there can be provided a lubricating oil composition, which can suppress increase in acid value and generation of sludge, and has low corrosivity to metals.

The % C_(A) is more preferably 1.0 or less, and still more preferably 0.5 or less, and the sulfur content is more preferably 30 ppm by mass or less.

Further, a viscosity index of the base oil is preferably 70 or more, more preferably 100 or more, and still preferably 120 or more. In the base oil having the viscosity index of 70 or more, change in the viscosity due to temperature change is small.

The lubricating oil composition of the present invention is required to contain an alkali metal borate or a hydrate thereof.

The alkali metal borate or the hydrate thereof used in the present invention is, in general, utilized as a fine particle dispersant which is easy to handle. Examples of the alkali metal borate or the hydrate thereof include compounds synthesized by the methods described in U.S. Pat. Nos. 3,929,650 and 4,089,790. For example, a fine particle dispersant of the alkali metal borate obtained by the following procedure can be given: carbonating neutral sulfonate of alkali metal or alkali earth metal under the presence of an alkali metal hydroxide, preferably additionally under the coexistence of an ashless dispersant such as succinimide, to thereby obtain perbasic sulfonate; and reacting boric acid therewith. The alkali metal used herein is desirably potassium, sodium, or the like.

As a specific example thereof, there can be given a fine particle dispersant having a particle diameter of about 0.3 μm or less, in which a hydrate of alkali metal borate represented by composition formula of KB₃O₅.H₂O is dispersed in neutral calcium sulfonate and succinimide.

In the present invention, the lubricating oil composition needs to contain those alkali metal borates or the hydrates thereof in an amount of 10 to 1,000 ppm by mass in terms of alkali metal based on a total amount of the composition. In the case where the amount is less than 10 ppm by mass, detergency may be unsatisfactory when the biofuel is mixed therein. Even in the case where the amount to be mixed exceeds 1,000 ppm by mass, a corresponding expansion in effect of the detergency cannot be observed when the biofuel is mixed therein, and dispersibility thereof may be decreased. Due to those reasons, the amount of the alkali metal borate or the hydrate thereof is preferably 50 to 500 ppm by mass.

In the lubricating oil composition of the present invention, it is preferred that, in addition to the alkali metal borate or the hydrate thereof (may be referred to as “component (A)”), at least one kind of compound selected from the following be mixed therewith: (B) a substituted hydroxyaromatic carboxylate derivative; (C) a phenol-based antioxidant; (D) an amine-based antioxidant; and (E) a molybdenum-based antioxidant.

The component (B) is at least one compound selected from substituted hydroxyaromatic carboxylate ester derivatives represented by formulae (I) and (II).

In the above-mentioned formulae (I) and (II), each of R¹, R², R³, R⁴, and R⁵ represents an organic group having 6 or more carbon atoms. Examples of the organic group having 6 or more carbon atoms include hydrocarbon groups having preferably 6 to 100 carbon atoms, more preferably 8 to 20 carbon atoms. Examples of the hydrocarbon groups include an alkyl group, an alkenyl group, a cycloalkyl group, a cycloalkenyl group and an aralkyl group, and those groups may have a non-hydrocarbon substituent and a hetero-atom in a chain or a ring. Specific examples of the hydrocarbon groups include hydrocarbon groups such as a hexyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a hexadecyl group, a triacontyl group, and groups derived from olefin polymers such as polyethylene, polypropylene, and polybutene. In the case where the substituted hydroxyaromatic carboxylate ester derivative having a low viscosity is desired, it is preferred that R¹, R², R³, R⁴, and R⁵ are substantially straight-chain hydrocarbon groups. R¹ and R² may be identical to or different from each other, and R³, R⁴, and R⁵ may be identical to or different from one another.

In the above-mentioned general formula (I), a, b, c, d, and e each represents an integer satisfying the relations of 1≦a≦3, 1≦b≦3, 0≦c≦3, 1≦d≦3, 1≦e≦3, 3≦(a+b+e)≦6, and 1≦(c+d)≦5. In the case where b represents 2 or 3, a plurality of R¹'s may be identical to or different from one another, and in the case where d represents 2 or 3, a plurality of R²'s may be identical to or different from one another.

In the above-mentioned general formula (II), f, g, h, i, j, k, and m each represent an integer satisfying the relations of 0≦f≦3, 0≦g≦3, 1≦(f+g)≦3, 0≦h≦4, 0≦i≦3, 1≦(h+i)≦6, 0≦j 3, 1≦k≦3, 1≦m 3, 0≦(f+h)≦4, 1≦(g+i+m)≦4, and 1≦(j+k)≦5. In the case where h represents 2, 3, or 4, a plurality of R³'s may be identical to or different from one another, and in the case where i represents 2 or 3, a plurality of R⁴'s may be identical to or different from one another. Moreover, in the case where k represents 2 or 3, a plurality of R⁵'s may be identical to or different from one another.

Specific examples of the substituted hydroxyaromatic carboxylate ester derivatives represented by the general formula (I) include (hexylhydroxybenzoic acid) hexylphenyl ester, (hexylhydroxybenzoic acid) dodecylphenyl ester, (octylhydroxybenzoic acid) octylphenyl ester, (nonylhydroxybenzoic acid) nonylphenyl ester, (nonylhydroxybenzoic acid) hexadecylphenyl ester, (dodecylhydroxybenzoic acid) nonylphenyl ester, (dodecylhydroxybenzoic acid) dodecylphenyl ester, (dodecylhydroxybenzoic acid) hexadecylphenyl ester, (hexadecylhydroxybenzoic acid) hexylphenyl ester, (hexadecylhydroxybenzoic acid) dodecylphenyl ester, (hexadecylhydroxybenzoic acid) hexadecylphenyl ester, (eicosylhydroxybenzoic acid) eicosylphenyl ester, (mixed alkylhydroxybenzoic acid having 11 to 15 carbon atoms) mixed alkylphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxybenzoic acid) dodecylphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxybenzoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] phenyl ester, (hexylhydroxybenzoic acid) hexylhydroxyphenyl ester, (octylhydroxybenzoic acid) octylhydroxyphenyl ester, (dodecylhydroxybenzoic acid) nonylhydroxyphenyl ester, (dodecylhydroxybenzoic acid) dodecylhydroxyphenyl ester, (hexadecylhydroxybenzoic acid) dodecylhydroxyphenyl ester, (hexadecylhydroxybenzoic acid) hexadecylhydroxyphenyl ester, (eicosylhydroxybenzoic acid) eicosylhydroxyphenyl ester, (mixed alkylhydroxybenzoic acid having 11 to 15 carbon atoms) mixed alkylhydroxyphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxybenzoic acid) dodecylhydroxyphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxybenzoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxyphenyl ester, (hexyldihydroxybenzoic acid) hexylphenyl ester, (nonyldihydroxybenzoic acid) nonylphenyl ester, (nonyldihydroxybenzoic acid) dodecylphenyl ester, (dodecyldihydroxybenzoic acid) nonylphenyl ester, (dodecyldihydroxybenzoic acid) dodecylphenyl ester, (hexadecyldihydroxybenzoic acid) hexadecylphenyl ester, (eicosyldihydroxybenzoic acid) hexadecylphenyl ester, (eicosyldihydroxybenzoic acid) eicosylphenyl ester, (mixed alkyldihydroxybenzoic acid having 11 to 15 carbon atoms) mixed alkylphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxybenzoic acid) dodecylphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxybenzoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atom, or a group derived from a polybutene having a number-average molecular weight of 400 or more] phenyl ester, (hexyldihydroxybenzoic acid) hexylhydroxyphenyl ester, (nonyldihydroxybenzoic acid) nonylhydroxyphenyl ester, (nonyldihydroxybenzoic acid) dodecylhydroxyphenyl ester, (dodecyldihydroxybenzoic acid) nonylhydroxyphenyl ester, (dodecyldihydroxybenzoic acid) dodecylhydroxyphenyl ester, (hexadecyldihydroxybenzoic acid) hexadecylhydroxyphenyl ester, (eicosyldihydroxybenzoic acid) hexadecylhydroxyphenyl ester, (eicosyldihydroxybenzoic acid) eicosylhydroxyphenyl ester, (mixed alkyldihydroxybenzoic acid having 11 to 15 carbon atoms) mixed alkylhydroxyphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxybenzoic acid) dodecylhydroxyphenyl ester, and (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxybenzoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxyphenyl ester.

On the other hand, specific examples of the substituted hydroxyaromatic carboxylate ester derivatives represented by the general formula (II) include (hexylhydroxynaphthoic acid) hexylphenyl ester, (hexylhydroxynaphthoic acid) hexadecylphenyl ester, (nonylhydroxynaphthoic acid) nonylphenyl ester, (dodecylhydroxynaphthoic acid) dodecylphenyl ester, (hexadecylhydroxynaphthoic acid) hexadecylphenyl ester, (dodecylhydroxynaphthoic acid) eicosylphenyl ester, (eicosylhydroxynaphthoic acid) eicosylphenyl ester, (mixed alkylhydroxynaphthoic acid having 11 to 15 carbon atoms) mixed alkylphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxynaphthoic acid) dodecylphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxynaphthoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] phenyl ester, (hexylhydroxynaphthoic acid) dodecylhydroxyphenyl ester, (octylhydroxynaphthoic acid) dodecylhydroxyphenyl ester, (dodecylhydroxynaphthoic acid) dodecylhydroxyphenyl ester, (dodecylhydroxynaphthoic acid) hexadecylhydroxyphenyl ester, (hexadecylhydroxynaphthoic acid) hexadecylhydroxyphenyl ester, (hexadecylhydroxynaphthoic acid) eicosylhydroxyphenyl ester, (mixed alkylhydroxynaphthoic acid having 11 to 15 carbon atoms) mixed alkylhydroxyphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxynaphthoic acid) dodecylhydroxyphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxynaphthoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxyphenyl ester, (hexyldihydroxynaphthoic acid) hexylphenyl ester, (hexyldihydroxynaphthoic acid) hexadecylphenyl ester, (nonyldihydroxynaphthoic acid) nonylphenyl ester, (dodecyldihydroxynaphthoic acid) dodecylphenyl ester, (dodecyldihydroxynaphthoic acid) eicosylphenyl ester, (hexadecyldihydroxynaphthoic acid) hexadecylphenyl ester, (eicosyldihydroxynaphthoic acid) eicosylphenyl ester, (mixed alkyldihydroxynaphthoic acid having 11 to 15 carbon atoms) mixed alkylphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxynaphthoic acid) dodecylphenyl ester, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxynaphthoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] phenyl ester, (hexyldihydroxynaphthoic acid) dodecylhydroxyphenyl ester, (octyldihydroxynaphthoic acid) dodecylhydroxyphenyl ester, (dodecyldihydroxynaphthoic acid) dodecylhydroxyphenyl ester, (dodecyldihydroxynaphthoic acid) hexadecylhydroxyphenyl ester, (hexadecyldihydroxynaphthoic acid) hexadecylhydroxyphenyl ester, (hexadecyldihydroxynaphthoic acid) eicosylhydroxyphenyl ester, (mixed alkyldihydroxynaphthoic acid having 11 to 15 carbon atoms) mixed alkylhydroxyphenyl esters having 11 to 15 carbon atoms, (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxynaphthoic acid) dodecylhydroxyphenyl ester, and (long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] dihydroxynaphthoic acid) long-chain alkyl [e.g., a group derived from a polydecene having 30 or more carbon atoms, or a group derived from a polybutene having a number-average molecular weight of 400 or more] hydroxyphenyl ester.

Of those substituted hydroxyaromatic carboxylate ester derivatives, more preferable examples are compounds represented by the following general formula (III):

where R¹, R², b, d, and e are as defined above, and the sum of b and e is 2 to 5, and compounds represented by the following general formula (III′):

where R³, R⁴, R⁵, h, k, and m are as defined above, n represents 0, 1 or 2, the sum of h and n is 1 to 6, and the sum of m and n is 1 to 3.

The above-mentioned substituted hydroxyaromatic carboxylate ester derivative may be composed of one kind of compound or two or more kinds of compounds represented by the general formula (I), or may be composed of one kind of compound or two or more kinds of compounds represented by the general formula (II). Alternatively, the substituted hydroxyaromatic carboxylate ester derivative may be composed of one or more compounds represented by the general formula (I) and one or more compounds represented by the general formula (II). An amount of the component (B) is preferably 0.5 to 30 mass % and more preferably 1 to 10 mass %, based on a total amount of the composition. When the amount of the component (B) is in the above range, there are effects of enhancing detergency of the composition and improving oxidation stability even in the case where the biofuel is mixed therein.

Preferable examples of the phenol-based antioxidant as a component (C) include: 2,6-di-tert-butyl-4-methylphenyl; 2,6-di-tert-butyl-4-ethylphenol; 2,4,6-tri-tert-butylphenol; 2,6-di-tert-butyl-4-hydroxymethylphenyl; 2,6-di-tert-butylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-butyl-4-(N,N-dimethylaminomethyl)phenol; 2,6-di-tert-amyl-4-methylphenol; 4,4′-methylenebis(2,6-di-tert-butylphenol), 4,4′-bis(2,6-di-tert-butylphenol), 4,4′-bis(2-methyl-6-tert-butylphenol), 2,2′-methylenebis(4-ethyl-6-tert-butylphenol), 2,2′-methylenebis(4-methyl-6-tert-butylphenol), 4,4′-butylidenebis(3-methyl-6-tert-butylphenol), 4,4′-isopropylidenebis(2,6-di-tert-butylphenol), 2,2′-methylenebis(4-methyl-6-nonylphenol), 2,2′-isobutylidenebis(4,6-dimethylphenol), 2,2′-methylenebis(4-methyl-6-cyclohexylphenol), 2,4-dimethyl-6-tert-butylphenol, 4,4′-thiobis(2-methyl-6-tert-butylphenol), 4,4′-thiobis(3-methyl-6-tert-butylphenol), 2,2′-thiobis(4-methyl-6-tert-butylphenol), bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide, bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide, 2,2′-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)_(p) ropionate], tridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and octyl-3-(3-methyl-5-tert-butyl-4-hydroxyphenyl)propionate.

As the component (C), one kind of the above-mentioned phenol-based antioxidants may be used alone, or two or more kinds thereof may be used in combination. An amount of the component (C) is selected, from the viewpoints of a balance between effect and economy and the like, preferably in a range of 0.05 to 3.0 mass % and more preferably in a range of 0.2 to 2.0 mass %, based on a total amount of the lubricating oil composition.

As the amine-based antioxidant serving as a component (D), any appropriate antioxidant may be selected from known amine-based antioxidants which are conventionally used as antioxidants for lubricating oil. Examples of the amine-based antioxidant as a component (D) include diphenylamine-based antioxidants, specifically, diphenylamine; alkylated dipehnylamines of alkyl groups having 3 to 20 carbon atoms such as a monooctyl diphenylamine; monononyldiphenylamine, 4,4′-dibutyl diphenylamine, 4,4′-dihexyl diphenylamine, 4,4′-dioctyl diphenylamine, 4,4′-dinonyl diphenylamine, tetrabutyl diphenylamine, tetrahexyl diphenylamine, tetraoctyl diphenylamine, and tetranonyl diphenylamine; napthylamine-based antioxidants, specifically, α-napthylamine and phenyl-α-napthylamine; and alkyl substituted phenyl-α-naphtyl amines having 3 to 20 carbon atoms such as butylphenyl-α-napthylamine, hexylphenyl-α-napthylamine, octylphenyl-α-napthylamine, and nonylphenyl-α-napthylamine. Of those, diphenylamine-based antioxidants are more favorable than napthylamine-based antioxidants in terms of effectiveness, alkylated diphenylamines of alkyl groups having 3 to 20 carbon atoms are particularly favorable, and 4,4′-di(C₃ to C₂₀ alkyl)diphenylamine is most favorable.

As the component (D), one kind of the above-mentioned amine-based antioxidants may be used alone, or two or more kinds thereof may be used in combination. An amount of the component (D) is selected, from the viewpoints of a balance between effect and economy and the like, preferably in a range of 0.05 to 3.0 mass % and more preferably in a range of 0.2 to 2.0 mass %, based on a total amount of the lubricating oil composition.

As the molybdenum-based antioxidant serving as a component (E), a molybdenum-amine complex can be preferably exemplified. As the molybdenum-amine complex, the following compound can be used: a hexavalent molybdenum compound, more specifically, a compound obtained by reacting molybdenum trioxide and/or molybdic acid with an amine compound, a compound obtained by a production method described in JP 2003-252887 A, for example.

Examples of the amine compound to be reacted with the hexavalent molybdenum compound are not particularly limited and specifically includemonoamines, diamines, andalkanolamines. More specifically, alkylamines of alkyl groups having 1 to 30 carbon atoms such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine, dipentadecylamine, dihexadecylamine, diheptadecylamine, dioctadecylamine, methylethylamine, methylpropylamine, methylbutylamine, ethylpropylamine, ethylbutylamine, and propylbutylamine (those alkyl groups may be in a straight chain form or in a branched chain form); alkenylamines of alkenyl groups having 2 to 30 carbon atoms such as ethenylamine, propenylamine, butenylamine, octenylamine, and oleylamine (those alkenyl groups may be in a straight chain form or in a branched chain form); alkanolamines of alkanol groups having 1 to 30 carbon atoms such as methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, hexanolamine, heptanolamine, octanolamine, nonanolyamine, methanolethanolamine, methanolpropanolamine, methanolbutanolamine, ethanolpropanolamine, ethanolbutanolamine, and propanolbutanolamine (those alkanol groups may be in a straight chain form or in a branched chain form); alkylenediamines of alkylene groups having 1 to 30 carbon atoms such as methylenediamine, ethylenediamine, propylenediamine, and butylenediamine; polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; compounds having alkyl groups or alkenyl groups having 8 to 20 carbon atoms in the above monoamines, diamines, and polyamines such as undecyl diethylamine, undecyl diethanolamine, dodecyl dipropanolamine, oleyl diethanolamine, oleyl propylenediamine and stearyl tetraethylenepentamine; heterocyclic compounds such as imidazoline; alkyleneoxide additives of those compounds; and mixtures thereof. Of those amine compounds, primary amines, secondary amines, and alkanol amines are preferable.

A carbon number of the hydrocarbon group which those amine compounds each have is preferably 4 or more, more preferably 4 to 30, and particularly preferably 8 to 18. When the carbon number of the hydrocarbon group of the amine compound is less than 4, solubility thereof tends to deteriorate. Further, when the carbon number of the amine compound is 30 or less, a molybdenum content in the molybdenum-amine complex can be relatively increased, and thus, small amount thereof can enhance the effect. One kind of those amine compounds may be used alone, or two or more kinds thereof may be used in combination.

Regarding a reaction ratio of the hexavalent molybdenum compound to the amine compound, a molar ratio of Mo atom of the molybdenum compound is, with respect to 1 mol of the amine compound, preferably 0.7 to 5, more preferably 0.8 to 4, and still more preferably 1 to 2.5. A reaction method is not particularly limited, and a conventionally known method, that is, a method described in JP 2003-252887 A, for example, can be adopted.

In the present invention, as the molybdenum-based antioxidant, a sulfur-containing molybdenum complex of succinimide described in JP 03-22438 A, JP 2004-2866 A, or the like other than the molybdenum-amine complex can also be used.

As the component (E), one kind of the above-mentioned molybdenum-based antioxidants may be used alone, or two or more kinds thereof may be used in combination. An amount of the component (E) is selected, from the viewpoints of a balance between effect and economy and the like, preferably in a range of 0.05 to 3.0 mass %, more preferably in a range of 0.1 to 2.0 mass %, and still more preferably in a range of 0.2 to 2.0 mass %, based on a total amount of the lubricating oil composition.

It is preferred that the lubricating oil composition of the present invention include, in addition to the component (A), at least one kind of compound selected from the components (B) to (E). By containing at least one kind of those compounds, detergency and oxidation stability when the biofuel is mixed therein can be further enhanced.

Of the above, preferred embodiments of the present invention include the following:

(1) base oil+(A);

(2) base oil+(A)+(B);

(3) base oil+(A)+(C) and/or (D);

(4) base oil+(A)+(B) and/or (D); and

(5) base oil+(A)+(B)+(C) and/or (D)+(E).

In particular, the embodiments of (2), (4), and (5), that is, the embodiments containing the component (B) is preferred from the viewpoint of further enhancing detergency and oxidation stability of the lubricating oil composition when the biofuel is mixed therein.

The lubricating oil composition of the present invention can be appropriately mixed with, as long as the object of the present invention is not adversely affected, other additives as required, such as a viscosity index improver, a pour-point depressant, a detergent dispersant, another antioxidant, an antiwear agent or an extreme pressure agent, a friction reducing agent, a dispersant, a rust preventives, a surface active agent or a demulsifier, and defoaming agent.

Examples of the viscosity index improver include polymethacrylate, dispersion-type polymethacrylate, an olefin-based copolymer (e.g., ethylene-propylene copolymer), a dispersion-type olefin-based copolymer, and styrene-based copolymer (e.g., styrene-diene copolymer or styrene-isoprene copolymer).

An amount of the viscosity index improver is, from the viewpoint of the effect, in general, preferably 0.5 to 15 mass % and more preferably 1 to 10 mass %, based on a total amount of the lubricating oil composition.

As the pour-point improver, polymethacrylate having a weight average molecular weight of about 5,000 to 50,000 and the like can be exemplified.

An amount of the pour-point depressant is, from the viewpoint of the effect, in general, preferably 0.1 to 2 mass % and more preferably 0.1 to 1 mass %, based on a total amount of the lubricating oil composition.

As the detergent dispersant, an ashless dispersant or a metal-based detergent can be used.

As the ashless dispersant, any appropriate ashless dispersant which is used for lubricating oil can be used, and for example, a monotype succinimide compound represented by the general formula (IV) or a bis-type succinimide compound represented by the general formula (V) is given:

-   -   where: R⁶, R⁸, and R⁹ each represent an alkenyl group having a         number average molecular weight of 500 to 4,000 or an alkyl         group having a number average molecular weight of 500 to 4,000,         and R⁸ and R⁹ may be identical to or different from each other;

R⁶, R⁸, and R⁹ each have a number average molecular weight of preferably 1,000 to 4,000; and

R⁷, R¹⁰, and R¹¹ each represent an alkylene group having 2 to 5 carbon atoms, R¹⁰ and R¹¹ may be identical to or different from each other, r represents an integer of 1 to 10, and s represents 0 or an integer of 1 to 10.

When the number average molecular weight of each of R⁶, R⁸, and R⁹ is less than 500, solubility into the base oil decreases, and when the number average molecular weight exceeds 4,000, detergency lowers and the intended performance may not be obtained.

Further, r represents preferably 2 to 5 and more preferably 3 to 4. When r is less than 1, detergency deteriorates, and when r is 11 or more, solubility with respect to the base oil may deteriorate.

In the general formula (V), s represents preferably 1 to 4 and more preferably 2 to 3.

When s is in the above range, the fact is preferred from the viewpoints of detergency and solubility with respect to the base oil.

Examples of the alkenyl group include a polybutenyl group, a polyisobutenyl group, and an ethylene-propylene copolymer, and the alkyl group is the group obtained by subjecting those to hydrogenation.

As a typical example of a favorable alkenyl group, a polybutenyl group or a polyisobutenyl group is given.

The polybutenyl group can be obtained by polymerizing a mixture of 1-butene and isobutene or a high-purity isobutene.

Further, as a typical example of a favorable alkyl group, a polybutenyl group or a polyisobutenyl group each of which is subjected to hydrogenation is given.

The alkenyl oralkyl succinimide compound can be produced, in general, by reacting the following with polyamine: an alkenyl succinic acid anhydride obtained by a reaction of polyolefin and maleic anhydride; or an alkyl succinic acid anhydride obtained by subjecting the alkenyl succinic acid anhydride to hydrogenation.

The monotype succinimide compound and the bis-type succinimide compound can be produced by changing a reaction ratio of the alkenyl succinic acid anhydride or the alkyl succinic acid anhydride with the polyamine.

As a olefin monomer forming the above polyolefin, one kind of α-olefin having 2 to 8 carbon atoms or two or more kinds thereof in a mixture can be used, and the mixture of 1-butene and isobutene can be favorably used.

Examples of the polyamine include: diamines such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; and piperazine derivatives such as aminoethyl piperazine.

Further, aside from the alkenyl or alkyl succinimide compound, a boron derivative thereof and/or a modified product thereof with organic acid may be used.

The boron derivative of the alkenyl or alkyl succinimide compound which is produced by an ordinary method can be used.

For example, the boron derivative of the alkenyl or alkyl succinimide compound can be obtained by imidization performed as follows: reacting the polyolefin with maleic anhydride to thereby obtain an alkenyl succinic acid anhydride; and then reacting the alkenyl succinic acid anhydride with an intermediate which is obtained by a react ion between the above polyamine and a boron compound such as boron oxide, boron halide, boric acid, boric acid anhydride, borate ester, or ammonium salt of boric acid.

A boron content in the boron derivative is not particularly limited, but is generally 0.05 to 5 mass and preferably 0.1 to 3 mass as boron.

An amount of the monotype succinimide compound represented by the general formula (IV) or the bis-type succinimide compound represented by the general formula (V) is, in general, preferably 0.5 to 15 mass % and more preferably 1 to 10 mass %, based on a total amount of the lubricating oil composition.

When the amount is less than 0.5 mass %, it is difficult to exhibit the effect thereof, and even when the amount exceeds 15 mass %, the effect corresponding to the amount may not be obtained.

Further, one kind of the succinimide compound may be used alone, or two or more kinds thereof may be used in combination, as long as the compound contains the above defined amount.

As the metal-based detergent, any appropriate alkali earth metal-based detergent which is used for lubricating oil can be used, and examples thereof include: alkali earth metal sulfonates; alkali earth metal phenates; alkali earth metal salicylates; and a mixture of two kinds or more selected therefrom.

Examples of the alkali earth metal sulfonates include alkali earth metal salts, particularly magnesium salts and/or calcium salts, of alkyl aromatic sulfoante obtained by sulfonating an alkyl aromatic compound having a molecular-weight of 300 to 1,500, preferably 400 to 700. Of those, calcium salts are preferably used.

Examples of the alkali earth metal phenates include alkali earth metal salts, particularly magnesium salts and/or calcium salts, of alkylphenol, alkylphenol sulfide, and a mannich reaction product of alkylphenol. Of those, calcium salts are preferably used.

Examples of the alkali earth metal salicylate include alkali earth metal salts, particularly magnesium salts and/or calcium salts, of alkyl salicylate. Of those, calcium salts are preferably used.

An alkyl group which forms the alkali earth metal-based detergent is preferably an alkyl group having 4 to 30 carbon atoms, and more preferably a linear or branched alkyl group having 6 to 18 carbon atoms, those of which may be linear or branched.

Those may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group.

In addition, examples of the alkali earth metal sulfonate, alkali earth metal phenate, and alkali earth metal salicylate include neutral alkali earth metal sulfonates, neutral alkali earth metal phenates, and neutral alkali earth metal salicylates each obtained by causing an alkyl aromatic sulfonic acid, an alkyl phenol, an alkyl phenol sulfide, a Mannich reaction product of alkyl phenol, an alkyl salicylic acid, or the like to react directly with an alkali earth metal base such as an oxide or hydroxide of alkali earth metals such as magnesium and/or calcium, or each obtained by making an alkali metal salt such as sodium salts or potassium salts of an alkyl aromatic sulfonic acid, an alkyl phenol, an alkyl phenol sulfide, a Mannich reaction product of alkyl phenol, an alkyl salicylate, or the like, and then substituting the obtained salt with an alkali earth metal salt. Examples thereof also include basic alkali earth metal sulfonates, basic alkali earth metal phenates, and basic alkali earth metal salicylates each obtained by heating a neutral alkali earth metal sulfonate, a neutral alkali earth metal phenate, or a neutral alkali earth metal salicylate and an excess amount of an alkali earth metal salt or an alkali earth metal base in the presence of water, and include perbasic alkali earth metal sulfonates, perbasic alkali earth metal phenates, and perbasic alkali earth metal salicylates each obtained by causing a neutral alkali earth metal sulfonate, a neutral alkali earth metal phenate, or a neutral alkali earth metal salicylate to react with a carbonate or a borate of alkali earth metals in the presence of carbon dioxide gas.

Examples of the metal-based detergent of the present invention which may be used include the above neutral salts, basic salts, perbasic salts, and mixtures thereof, and particularly mixtures of neutral sulfonate with one or more kinds of perbasic salicylates, perbasic phenates, and perbasic sulfonates are preferable in terms of detergency and wear resistance.

In the present invention, a total base number of the metal-based detergent is generally 10 to 500 mg KOH/g and preferably 15 to 450 mg KOH/g, and it is preferred to use one kind selected from the above or two or more kinds selected therefrom in combination.

Note that the total base number used herein refers to a total base number obtained by potentiometric titration (basic number/perchloric acid method) measured in accordance with Section 7 of JIS K 2501 “Petroleum products and lublicants—Determination of neutralization number”.

Further, as the metal-based detergent of the present invention, a metal ratio thereof is not particularly limited, and in general, one kind of the detergent having a metal ratio of 20 or less may be used alone, or two or more kinds thereof may be used in combination. However, it is preferred that a metal-based detergent having a metal ratio of preferably 3 or less, more preferably 1.5 or less, and particularly preferably 1.2 or less be an essential component, because of its excellence in oxidation stability, base number maintaining property, high temperature detergency, and the like.

Note that the metal ratio used herein is represented by valence of metal element in a metal-based detergent×metal element content (mol %)/soap group content (mol %), and the metal element means calcium, magnesium, and the like, and the soap group means a sulfonateic acid group, a phenol group, a salicylic acid group, and the like.

A metal-based detergent is, in general, commercialized and available in a form diluted with light lubricating base oil or the like, and in general, using a metal-based detergent having a metallic content of 1.0 to 20 mass %, preferably 2.0 to 16% by mass is desirable.

An amount of the metal-based detergent is, in general, preferably 0.01 to 20 mass % and more preferably 0.1 to 10 mass %, based on a total amount of the lubricating oil composition.

When the amount is less than 0.01 mass %, it is difficult to exhibit the effect thereof, and when the amount exceeds 20 mass %, the effect corresponding to the amount may not be obtained.

Further, one kind of the metal-based detergent may be used alone, or two or more kinds thereof may be used in combination, as long as the detergent is contained in the above defined amount.

Examples of other antioxidants include sulfur-based antioxidants.

Examples of the sulfur-based antioxidants include phenothiazine, pentaerythritol-tetrakis(3-laurylthiopropionate), didodecylsulfide, dioctadecylsulfide, didodecylthiodipropionate, dioctadecyl thiodipropionate, dimyristyl thiodipropionate, dodecyloctadecyl thiodipropionate, and 2-mercaptobenzoimidazol.

An amount of the sulfur-basedantioxidant is, ingeneral, preferably 0.1 to 5 mass and more preferably 0.1 to 3 mass %, based on a total amount of the lubricating oil composition.

Examples of the antiwear agent and the extreme pressure agent include: compounds containing sulfur such as zinc dithiophosphate, zinc phosphate, zinc dithiocarbamate, disulfides, sulfurized olefins, sulfurized fats and oils, sulfurized esters, thiocarbonates, thiocarbamates, and polusulfides; compounds containing phosphorus such as phosphite esters, phosphate esters, phosphonate esters, and amine salts or metal salts thereof; and antiwear agents containing sulfur and phosphorus such as thiophosphite esters, thiophosphate esters, thiophosphonate esters, and amine salts or metal salts thereof.

As the friction reducing agent, any appropriate compound which is generally used as a friction reducing agent for lubricating oil can be used, and an example thereof includes an asheless friction reducing agent which has at least one alkyl group or alkenyl group having 6 to 30 carbon atoms in a molecule thereof, such as aliphatic acid ester, aliphatic acid amide, aliphatic acid, aliphatic alcohol, aliphatic amine, and aliphatic ether.

An amount of the friction reducing agent is, in general, preferably 0.01 to 2 mass % and more preferably 0.1 to 1 mass %, based on a total amount of the lubricating oil composition.

Examples of the metal deactivating agent include compounds such as benzotriazole-based compounds, tolyltriazol-based compounds, thiadiazole-based compounds, and imidazole-based compounds.

An amount of the metal deactivating agent is, in general, preferably 0.01 to 3 mass % and more preferably 0.01 to 1 mass %, based on a total amount of the lubricating oil composition.

Examples of the rust preventives include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinate esters, and polyvalent alcohol esters.

An amount of the rust preventives is, from the viewpoint of effect, in general, preferably about 0.01 to 1 mass % and more preferably 0.05 to 0.5 mass %, based on a total amount of the lubricating oil composition.

Examples of the surface active agent and the demulsifier include polyalkylene glycol-based non-ionic surface active agents such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

An amount of the surface active agent or the demulsifier is, in general, preferably 0.01 to 3 mass % and more preferably 0.01 to 1 mass %, based on a total amount of the lubricating oil composition.

Examples of the defoaming agent include silicone oil, fluorosilicone oil, and fluoroalkyl ether. An amount of the defoaming agent is, from the viewpoint of a balance between deforming effect and economy and the like, preferably 0.0005 to 0.5 mass % and more preferably 0.001 to 0.2 mass %, based on a total amount of the lubricating oil composition.

In the lubricating oil composition of the present invention, the sulfated ash content is preferably 1.2 mass % or less and more preferably 1.1 mass % or less. When the sulfated ash content is less than 1.2 mass %, performance deterioration of a catalyst purging exhaust gas can be suppressed. Further, when the sulfated ash content is applied to a diesel engine equipped with DPF, an amount of ash adhered to DPF becomes small, which enables lifetime of DPF to increase.

In the lubricating oil composition of the present invention, in addition, the sulfur content is preferably 0.5 mass % or less, more preferably 0.3 mass % or less, and still more preferably 0.2 mass % or less, based on a total amount of the composition. When the sulfur content is 0.5 mass % or less, performance deterioration of a catalyst purging exhaust gas can be suppressed effectively.

In the lubricating oil composition of the present invention, a phosphorus content is preferably 0.12 mass % or less and more preferably 0.1 mass % or less, based on a total amount of the composition. When the phosphorus content is 0.12 mass % or less, performance deterioration of a catalyst purging exhaust gas can be suppressed effectively.

The lubricating oil composition of the present invention contains a predetermined amount of the component (A), and therefore, the composition is excellent in detergency of engine parts such as piston, even in the case where the composition is used for an internal combustion engine of biofuel-burning type. Particularly when the component (B) is contained in a predetermined amount in addition to the component (A), the lubricating oil composition of the present invention is additionally excellent in detergency and oxidation stability at high temperature.

EXAMPLES

Next, the present invention is described in more detail by way of examples and comparative examples, but is not limited to those examples. Note that property and performance of the lubricating oil composition for an internal combustion engine were determined by the following methods.

(1) Kinematic Viscosity

The kinematic viscosity was determined in accordance with JIS K 2283.

(2) Contents of Calcium, Potassium, Boron, and Phosphorus

The contents of calcium, potassium, boron, and phosphorus were determined in accordance with JIS-5S-38-92.

(3) Nitrogen Content

The nitrogen content was determined in accordance with JIS K 2609.

(4) Contents of Molybdenum and Zinc

The contents of molybdenum and zinc were determined in accordance with JIS-5S-38-92.

(5) Sulfur Content

The sulfur content was determined in accordance with JIS K 2541.

(6) Sulfated Ash Content

The sulfated ash content was determined in accordance with JIS K 2272.

(7) NOACK Test

An amount of evaporation under NOACK test was determined in accordance with ASTM D 5800 and in the conditions of 250° C. and 1 hour.

(8) Hot Tube Test

As a lubricating oil composition for the test, a mixed oil in which 5 mass of biofuel (fuel obtained by transesterification of rapeseed oil with methyl alcohol) with respect to the above-mentioned respective lubricating oil compositions (new oil) was mixed was used, in consideration of the mixing ratio of fuel to lubricating oil inside the internal combustion engine. A test temperature was set to 290° C., and other conditions were set and determined in accordance with JPI-5S-55-99. Further, grades after the test was evaluated in accordance with JPI-5S-55-99, into 11 grades with respect to lacquer adhered to a test tube, from 0 point (black) to 10 points (colorless). It shows that the larger the number, the smaller the amount of deposit, which means detergency thereof is satisfactory. Note that, as a reference, the same test was performed except that only the new oil was used. Further, the hot tube test is sometimes influenced by the amount of the viscosity index improver, and therefore, a fixed amount of the viscosity index improver was used for each of examples and comparative examples.

(9) Oxidation Stability Test

The oxidation stability test of the lubricating oil composition for an internal combustion engine was performed in accordance with JIS K 2514-1996, in a same manner as the item (7) by using a mixed oil in which 5 mass % of biofuel (fuel obtained by transesterification of rapeseed oil with methyl alcohol) with respect to the above-mentioned respective lubricating oil compositions (new oil) was added.

The composition was oxidized under the following test conditions, and kinematic viscosities at 100° C. of the composition before the test (new oil) and of the composition after the test were determined, to thereby obtain a viscosity increasing rate in %. It shows that the smaller the viscosity increasing rate, the more excellent in oxidation stability.

(Test Conditions)

Test temperature: 165.5° C., number of revolutions: 1,300 rpm, test time: 168 hours, catalyst: copper plate and iron plate

Examples 1 to 5 and Comparative Examples 1 to 3

The lubricating oil compositions were prepared by mixing base oils and additives shown in Table 1 in ratios shown in Table 1. The performances and properties thereof are shown in Table 1.

TABLE 1 Ex- Ex- Ex- Ex- Comparative Comparative Comparative ample 1 ample 2 ample 3 ample 4 Example 5 Example 1 Example 2 Example 3 Mixing Base oil¹⁾ 80.71 80.51 80.31 81.51 81.31 80.81 81.81 82.61 ratio (wt %) (A) alkali metal borate hydrate²⁾ 0.10 0.30 0.50 0.30 0.50 — — — (B) aromatic carboxylate ester³⁾ 1.00 1.00 1.00 — — 1.00 — — (C) phenol type antioxidant⁴⁾ 0.50 0.50 0.50 0.50 0.50 0.50 0.50 — (D) amine type antioxidant⁵⁾ 0.20 0.20 0.20 0.20 0.20 0.20 0.20 — (E) Molybdenum-based antioxidant⁶⁾ 0.10 0.10 0.10 0.10 0.10 0.10 0.10 — Viscosity index improver⁷⁾ 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 Pour-point depressant⁸⁾ 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Metal-based detergent⁹⁾ 2.82 2.82 2.82 2.82 2.82 2.82 2.82 2.82 polybutenyl succinimide-1¹⁰⁾ 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 polybutenyl succinimide-2¹¹⁾ 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 zinc dialkyldithio phosphoric acid¹²⁾ 1.22 1.22 1.22 1.22 1.22 1.22 1.22 1.22 copper corrosion inhibitor¹³⁾ 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 silicon based defoaming agent etc.¹⁴⁾ 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Property of Ca content wt % 0.22 0.22 0.22 0.22 0.22 0.22 0.22 0.22 composition potassium content (weight ppm) 38 120 203 118 201 0 0 0 boron content (weight ppm) 67 203 338 205 341 0 0 0 nitrogen content wt % 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.07 molybdenum content (wt %) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00 sulfur content (wt %) 0.22 0.22 0.22 0.22 0.22 0.22 0.22 0.22 phosphorus content (wt %) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 zinc content (wt %) 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 sulfated ash content (wt %) 0.97 1.01 1.04 1.01 1.04 0.96 0.96 0.96 Performance hot tube test new oil 3 9 9 9 9 1 1 1 (290° C.) new oil + biofuel 1 8 9 4 6 0 0 0 (5 wt %) Oxidation 100° C. Before test 8.963 8.961 8.972 8.836 8.846 8.960 8.751 8.636 stability test kinematic After test 9.796 9.876 9.584 10.86 10.88 9.824 10.57 Solidified* (new oil + biofuel viscosity 5 wt %) (mm²/s) viscosity increasing 109.3 110.2 106.8 122.9 123.0 109.6 120.8 — rate (%) [Notes] ¹⁾Base oil: hydrogenated refining base oil (kinematic viscosity at 40° C. = 21 mm²/s, kinematic viscosity at 100° C. = 4.5 mm²/s, viscosity index = 127, % C_(A) = 0, sulfur content ≦ less than 20 ppm by mass, amount of evaporation under NOACK test = 13.3 mass %) ²⁾alkali metal borate hydrate: fine particle dispersant (borate content = 6.8 mass %, potassium content = 4.0 mass %) ³⁾aromatic carboxylate ester: dodecyl salicylate dodecylphenyl ester ⁴⁾phenol-based antioxidant: octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ⁵⁾amine-based antioxidant: dialkyldiphenylamine (nitrogen content = 4.62 mass %) ⁶⁾molybdenum-based antioxidant: trade name “SAKURALUBE 710” (manufactured by ADEKA corporation), molybdenum content = 10 mass %, nitrogen content = 1.3 mass %) ⁷⁾viscosity index improver: polymethacrylate (weight average molecular weight = 420,000, resin amount 39 mass %) ⁸⁾pour-point depressant: polyalkyl methacrylate (weight average molecular weight = 6,000) ⁹⁾metal-based detergent: perbasic caclium salicylate (base number (perchloric acid method) = 225 mg/KOH/g, Ca content = 7.8 mass %, sulfur content = 0.3 mass % ¹⁰⁾polybutenyl succinimide-1: mono type imide (average molecular weight of polybutenyl group = 1,000, nitrogen content = 1.76 mass % ¹¹⁾polybutenyl succinimide-2: bis type imide (average molecular weight of polybutenyl group = 2,000, nitrogen content = 0.99 mass % ¹²⁾zinc dialkyldithiophosphate: zinc content = 9.0 mass %, phosphorus content = 8.2 mass %, sulfur content = 17.1 mass %, alkyl group = mixture of secondary butyl group and secondary hexy group ¹³⁾copper corrosion inhibitor: 1-[N,N-bis(2-ethylhexyl)aminomethyl methylbenzo triazole] ¹⁴⁾silicon-based defoaming agent, rust preventives and surface active agent

According to Table 1, the lubricating oil composition of the present invention has excellent detergency of the lubricating oil composition of the new oil in hot tube test, and has a small decrease in performance thereof when the biofuel is added thereto. On the other hand, it is found that the lubricating oil compositions of Comparative Examples 1 to 3 which do not contain the component (A) of the present invention are inferior in detergency even when the compositions are lubricating oil compositions of new oil, and the decrease in performance thereof when the biofuel is added thereto is remarkable.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present invention can satisfactorily exhibit detergency even in the cases where the biofuel is mixed therein or ash content thereof is low. Therefore, the lubricating oil composition of the present invention can be effectively utilized as the lubricating oil composition used in an internal combustion engine employing a biofuel. 

1: A method of lubricating an internal combustion engine employing a fuel comprising at least one of a hydrogenated product of natural fats and oils, a transesterification product of natural fats and oils, and a hydrogenated product of a transesterification product of natural fats and oils, said method comprising lubricating said engine with a lubricating oil composition comprising: (A) an alkali metal borate or a hydrate thereof in an amount of 10 to 1,000 ppm by mass in terms of an alkali metal, based on a total amount of the lubricating oil composition; (C) a phenol-based antioxidant; (D) an amine-based antioxidant; and (E) a molybdenum-based antioxidant. 2: A method according to claim 1, wherein said lubricating oil composition further comprises: (B) at least one compound selected from the group consisting of: a substituted hydroxyaromatic carboxylate ester derivative represented by general formula (I):

where: R¹ and R², which are identical to or different from each other, each represent an organic group having 6 or more carbon atoms; a, b, c, d, and e each represent an integer satisfying relations of 1≦a≦3, 1≦b≦3, 0≦c≦3, 1≦d≦3, 1≦e≦3, 3≦(a+b+e)≦6, and 1≦(c+d)≦5; and when a plurality of R¹'s and a plurality of R²'s are present, each of the plurality of R¹'s and the plurality of R²'s are identical to or different from one another within the respective groups; and a substituted hydroxyaromatic carboxylate ester derivative represented by general formula (II):

where: R³, R⁴, and R⁵, which are identical to or different from one another, each represent an organic group having 6 or more carbon atoms; f, g, h, i, j, k, and m each represent an integer satisfying relations of 0≦f≦3, 0≦g≦3, 1≦(f+g)≦3, 0≦h≦4, 0≦i≦3, 1≦(h+i)≦6, 0≦j≦3, 1≦k≦3, 1≦m≦3, 0≦(f+h)≦4, 1≦(g+i+m)≦4, and 1≦(j+k)≦5; and when a plurality of R³'s, a plurality of R⁴'s, and a plurality of R⁵'s are present, each of the plurality of R³'s, the plurality of R⁴'s, and the plurality of R⁵'s are identical to or different from one another within the respective groups. 3: A method according to claim 2, wherein said lubricating oil composition further comprises a substituted hydroxyaromatic carboxylate ester derivative represented by general formula (I). 4: A method according to claim 2, wherein said lubricating oil composition further comprises a substituted hydroxyaromatic carboxylate ester derivative represented by general formula (II).
 5. The method according to claim 1, wherein said method is a method of lubricating an internal combustion engine employing a fuel comprising a hydrogenated product of natural fats and oils. 6: The method according to claim 1, wherein said method is a method of lubricating an internal combustion engine employing a fuel comprising a transesterification product of natural fats and oils. 7: The method according to claim 1, wherein said method is a method of lubricating an internal combustion engine employing a fuel comprising a hydrogenated product of a transesterification product of natural fats and oils. 